A pair of 8800 GT(2007) or 8800GTX(2006) cards would work, though I would go slightly ahead to 2009 and get a pair of 9800GTX+ cards instead and avoid any bumpgate issues 8000 series cards may have.
If you really want period correct then you will likely have issues due to the horrible solder nVidia was using during the 7000 and 8000 series GPUs, both gens are prone to issues that kills the GPU. So if you go with period correct you may want to stick to tested cards and make 100% sure they are working when you get them.
*If you cant find any 9800GTX+ cards at reasonable prices you can just grab a pair of Geforce GTS 250 cards as they are the 9800GTX+ cards rebadged, I have a pair of GTS250s and they are solid cards. (Got them rather cheap too as people just want to offload them and they are not big ticket cards)